The primary goal of this project is to address the diagnostic problem of identifying active filariasis infections in man. Serological immunoassays will be systematically developed and applied to the quantitation of circulating filarial antigen in order to provide more accurate discrimination between active and inactive filarial infections than has been possible with filarial-specific antibody assays. The project involves the following objectives: a) the development and optimization of three immunoassays which permit the quantitation of either free or immune-complexed (TC) filarial antigen in the serum of patients infected with Brugia malayi, Wuchereria bancrofti, or Onchocerca volvulus; b) examination of the specificity of these assays with cross-reactivity studies employing antigen extracts from other filarial species (D. immitis, O. cervicalis, and L. carinii) and other non-related human parasites (F. hepatica, A. lumbricoides, and S. mansoni); c) simultaneous development of analogous assays for detecting filarial antigen in a dog model (dog heartworm; D. immitis) which will be used to study the efficacy of each assay design in differentiating active from inactive or cured filarial infection; d) diagnosis and monitoring of filarial infections in man using two IC-antigen assays, the IC-Immunoradiometric Assay (IRMA) and the Radio-Polyethylene Glycol-Immunoassay (RPEGIA), and one free antigen assay, the Ag-IRMA; and e) comparison of results from these assays with values from non-specific immune-complex assays (Clq RIA and Conglutinin Binding RIA) and specific antibody assays (RAST and Protein A SPRIA) for their ability to determine active filarial infections in man.